Currently, Al electrolytic capacitors and laminated ceramic capacitors are widely used. Al electrolytic capacitors using electrolyte have problems such as electrolyte leakage. In addition, problems such as thermal contraction between electrodes and dielectric materials may occur since laminated ceramic capacitors are sintered in manufacturing. As a technology to resolve these problems, for example, the following Patent Literatures 1-3 each discloses a capacitor using porous Al2O3.
Japanese Patent Application Publication No. 2009-88034 (“Patent Literature 1”) discloses a capacitor formed of porous Al2O3 and a manufacturing method thereof where positive and negative electrodes are randomly allocated. According to the manufacturing method disclosed in the Patent Literature 1, the first anodic oxidation of a valve metal is performed to form holes with a desired depth (FIG. 2(C)), and then the second anodic oxidation is performed using a voltage higher than that used for the first anodic oxidation (FIG. 2(D)). As a pitch of holes formed during anodic oxidation is proportional to the applied voltage, a pitch of holes formed using a large voltage becomes larger. The holes formed during the second anodic oxidation are connected to a part of the holes formed during the first anodic oxidation. The bottoms of the holes formed during the second anodic oxidation are subsequently opened (FIGS. 2(E) and 2(F)), and platings are embedded therein whereby conductors are embedded only into the holes formed during the first anodic oxidation and connected to one of the holes formed during the second anodic oxidation but not into the holes that are not connected to any one of the holes formed during the second anodic oxidation (FIG. 3(A)). Next, an insulation cap is formed at the tip end of each of the embedded conductors using a method such as air gap, electro-deposition insulation, or anodic oxidation (FIG. 3(B)). Then, after the surplus dielectric layers (Al2O3) formed during the second anodic oxidation are removed, the holes formed during the first anodic oxidation are opened (FIGS.(C) and (D)). The same embedding procedures are performed from the opposite side (FIG. 4(A)). Thus, a capacitor structure having internal electrodes allocated on the front and rear surfaces (FIG. 4(C)).
Japanese Patent Application Publication No. 2009-21553 (“Patent Literature 2”) discloses a porous Al2O3 capacitor structure achieving low ESL by using nano-scale lithography. According to the manufacturing method described in the Patent Literature 2, a pair of interdigitate line patterns are formed on the surface of Al prior to performing anodic oxidation (FIG. 2(A)). Anodic oxidation onto the thus formed Al substrate creates a plurality of holes along with the line pattern (FIG. 2(B)). Then, conductive materials are embedded into the holes (FIGS. 2(C) and 3(A)) and the line patterns formed on the main surface are also filled with conductive materials (FIG. 3(C)). Thus, positive and negative electrodes are led out only from the main surface. Japanese Patent Application Publication No. 2009-49212 (“Patent Literature 3”) discloses a manufacturing method including filling line patterns formed on the main surface with conductive materials in a similar manner to that described above in connection with the Patent Literature 2 (FIGS. 10(A)-11(A) thereof), removing Al2O3 leaving the metals (surface electrodes and internal electrodes) (FIG. 11(B), and filling the clearances with dielectric materials different from Al2O3 (FIG. 11(C)). According to these structures, an electric current flowing in a positive or negative electrode flows in the opposite direction to the adjacent electrode having an opposite polarity, thereby reducing an inductance due to magnetic field offset.